This disk contains a backup of the last remaining copy of the Cray Operating System, the original operating system for the Cray-1 and Cray X-MP supercomputer line. The disk likely contains a binary image of COS 1.17 (the last revision of of the OS), as well as other unknown software, and initially belonged to a single-processor Cray X-MP machine. The disk was written in 1989. The machine's I/O Subsystem (IOS) would have likely booted from this disk, and then loaded the OS into main CPU memory. This was recovered from a CDC 9877 80 Megabyte disk pack, formatted with 5 heads/cylinder, 808 tracks, 512B/sector, 32 Sectors/track (~64 Megabytes after formatting).
We need help deciphering the file system of the image in order to bring us closer to finally being able to boot our FPGA-based Cray-1 (http://chrisfenton.com/homebrew-cray-1a/). If you make any progress / are interested in helping, contact Chris Fenton (firstname.lastname@example.org) and help us bring back the Cray-1!